There is a strong motivation to deploy smart, small in size, small in power consumption and low-cost sensors for vehicle parking support applications, in the following application scenarios and specific features:                a) Detection of obstacle distance at distances beyond 10 m.        b) Detection of obstacle angles related to sensor orientation, without inherently needing to process date from other sensors, as today is the case with ultrasound based parking systems.        c) Operation of the sensors integrated in the bumper or in other vehicle parts, not visible outside the vehicle, as commonly is the case with ultrasound parking systems.        d) Operation of the sensors connected with several identical sensors to provide more robust information for parking assistance.        e) Additional features to detect human or other living beings in the area intended for vehicle parking, with no extra hardware cost.        f) Additional features to detect vehicle vibrations, with no extra hardware cost.        g) Optional operation feature in case of several sensors are integrated in the bumper, in order to improve obstacle distance and angle accuracy, by processing data from more than one sensor integrated in the vehicle bumper.        
The majority of the state-of-the-art parking support sensors currently deployed are based on ultrasound technology. This approach has an inherent drawback, in that sensors integrated in the vehicle are visible. This is due to the nature of ultrasound propagation properties, where the bumper material does not allow for propagation of the ultrasound in an easy and usable manner. Furthermore, the external operation unit must procure additional processing power to provide accurate parking support information tithe driver. The driver is provided with the information about the existence of the obstacle, but is unable to get information if the obstacle could potentially be a living being, like a cat or a dog. On the other hand, these well-established ultrasound technology systems achieved huge production maturity and a low system cost.
Alternative solutions for parking support could be mm-wave radar systems, which are currently deployed mainly for long distance obstacle detections. In these operation modes, they must have high gain antennae, which implies larger size and other special features related to beam forming, tracking and object identifications. State of the art mm-wave radar IC structures in automotive frequency bands usually have 2 transmit chains and 4 receive chains. The cost of such system with antenna and the assembly is high, with mm-wave IC typically realized in SiGe BiCMOS technology. Integrated PLL and technology transfers to CMOS are currently being announced, to be designed on product level. Millimeter-wave radar systems could be integrated in the vehicle bumper, but having communication losses and system topologies of mm-wave sensors and methods of operation, do not allow for low system cost. At least not low enough to be a valuable replacement path for the ultrasound sensors. The number of transmit and receive channels is too high, power levels are too high, the dynamic range is not adjusted for special applications and a complicated signal processing is required.
The following published patents and patent applications show the relevance of the topic and the state-of-the-art in respect to mm-wave systems, as well as approaches for mm-wave radar system direction of arrival.
It may be observed that there are no radar-based sensor solutions reported, for systems able to detect both the distance and at the same time and in a simple manner, able to detect the angle of the obstacle, yet having only one down conversion chain or one Rx down conversion channel. Also, there are proposed radar sensor topology solutions reported, capable of additional features in detecting the obstacle's internal vibrations, resulting in the detection of living thing.
DE 102012201367, “The millimeter wave radar” introduces a millimeter-wave radar device with at least one millimeter wave circuit and at least one antenna, constructed as a module of a multi-layer multi-polymer board.
U.S. Pat. No. 7,782,251, “Mobile millimeter wave imaging radar system” introduces a short range complex millimeter wave imaging radar system, having scanned Tx and Rx antennae.
U.S. Pat. No. 7,379,020, “Apparatus and method for estimating direction of arrival of radio wave”, by Fujitsu, describes a system with heavy mathematical calculation necessary for the direction of arrival calculation.
U.S. Pat. No. 4,929,958, “High precision radar detection system and method” describes the systems with four transducers to accurately determine the azimuth angle of a radar emitting object.
U.S. Pat. No. 5,724,047, “Phase and time-difference precision direction finding system” by Hughes Electronics, describes the system using the time difference of arrival (TDOA) of the signal at the two antenna elements. TDOA is measured using leading edge envelope detection for simple pulsed signals and pre-detection correlation for phase and frequency modulated signals.
U.S. Pat. No. 8,779,969, “Radar device for detecting azimuth of target” by Denso, describes azimuth detection by analyzing echoes by spectrum performance, excited by frequency ramped signal, mixed by the excitation signal.
U.S. Pat. No. 6,011,514, “Means for extracting phase information for radio frequency direction of arrival”, describes the approach with processing the signals at IF frequency level, where the signals are pulsed based signals.
U.S. Pat. No. 5,657,027, “A Two dimensional interferometer array”, treats two dimensional problem approach using 4 receiving channels and specific digital processing.